A Comparison of Three Indophenol Blue Methods for Measuring Ammonium in Five Types of Soils in China

Three indophenol blue methods have been used to analyze ammounium-N in five typical soils in China. Method I and II, using the same catalyst of sodium nitroprusside but different quantity and types of reagents, are suggested by Soil Science Society of America (SSSA) and Soil Science Society of China (SSSC), respectively. Method III adopts acetone as the catalyst. It was shown that three methods yielded similar ammonium-N contents with each type of soil. But the use of sodium nitroprusside resulted in higher experimental sensitivity; and Method II by SSSC was recommended due to its lower cost.